Pt Electrocatalyst Prepared by Hydrothermal Reduction onto the Gas Diffusion Layer for High-Temperature Formic Acid and Ethanol Fuel PEMFC

Round 1

Reviewer 1 Report

Dear Authors,

Thank you for submitting your work to Catalysts. The experiment results of Direct Formic Acid Fuel Cells and Direct Ethanol Fuel Cells are well presented and discussed. The conclusion is well supported by the data. 

However, there is one problem should be explain. The power density curves in Figure 4 are not smooth. It seems there are noise and errors associated with the experiment. Did you collect the data after the fuel cell performance was stabilized after a few minutes holding at each voltage? Please explain about the fluctuated curves at the medium and high current density region in details. What are the reasons? Did you try any other test method to solve it? Otherwise, the test results are less convincing. 

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

The present work reports an alternative approach for the preparation of practical electrocatalysts for PEMFCs, based on the direct deposition of the active material on the gas diffusion electrode (GDL). Although there are a few works reported in the literature adopting similar strategies (e.g., 10.1021/jacsau.1c00015, 10.1039/D0CS00230E, 10.1016/j.matchemphys.2013.08.026, 10.1007/s10800-020-01474-5) the approach is still of significance due to its direct applicability in actual electrolyzer/fuel cell devices. Overall, the work reports some interesting results, however there are a few points need to be clarified/revised prior to consideration for publication (see detailed comments appended below).

Abstract

1. Page 1 (line 14): “diffusion layer”: The term “gas diffusion electrode – GDL” should be used instead. Please perform the appropriate changes throughout the manuscript.
2. Page 1 (line 15): “…ethylene glycol and ethanol atmospheres.”: This sentence needs to be rephrased since the term “atmospheres” implies the occurrence of the reaction under a gas atmosphere, which is obviously not the case here.
3. Page 1 (line 19): “…H3PO4-doped polybenzimidazole PEMFC…”: To be clearer for the reader, I would suggest rephrasing this sentence to something like “…high temperature PEMFC using a H3PO4-doped polybenzimidazole membrane as the solid electrolyte”.

Results and Discussion

1. Page 3 (line 110): “…the smallest particle size…”: The results in Fig.2 report the crystallite size as calculated from the XRD data and not the particle size. These two terms are different. A particle is general considered as an agglomerate of individual crystallites. Thorough TEM analysis is required to determine whether a particle is a single crystallite and not a compacted structure of crystallites (Scherrer’s formula is just an approximation). This distinction should be made in the text and both the crystallite and particles sizes should be given. The latter might be estimated by the SEM data.
2. Page 4 (line 120): “The necessary higher temperature for EG (160-200oC)…”: The authors need to explain in detail the effect of temperature in the synthesis of their catalysts, i.e., why EG requires higher temperature etc.
3. Page 5 (lines 136-138): “It is important…reducing agent.”: I strongly suggest including all the relevant data (spectroscopic, microscopic -if any- and electrochemical results) in an additional Supplementary Information file.
4. Page 7 (Fig.3): As it can be seen from the SEM micrographs presented in Fig.3, the degree of Pt particles dispersion on GDL is quite low and relatively large nanoparticles are formed. The latter is in contrast with the arguments presented above based on the crystallite sizes (see also comment #1). The authors should comment on these features. To provide further insights into the effect of the synthesis conditions on the degree of dispersion of the Pt particles and thus the electrochemically active surface area (EASA) of the catalyst, the following additional experiments should be conducted: (i) Cyclic voltammograms using a three-electrode cell in deaerated acidic solutions within the potential region defined by the onsets of HER and OER and (b) CO stripping in the same solutions as in (a) to calculate EASA. The values of the latter should be reported and discussed in the text based on the experimental conditions used, the SEM data etc. All these can be included in the SI. Finally, EDX maps would be also quite useful to probe the degree of dispersion of the catalyst on the GDL.
5. Page 7 (lines 146-148): “Both molecules may adsorb…structure.”: This needs to be clarified. At first, the authors should provide indications about the allegedly (strong) adsorption of glycolic and oxalic acids on Pt (e.g., relevant references should be included). Furthermore, if such a phenomenon occurs, I would expect that the areas on which the molecules are adsorbed would be deactivated and hence excluded from the reaction. Do the authors imply a similar and/or synergetic result between the aforementioned acids and CTAB towards the controlled growth of the particles?
6. Page 7 (lines 148-152): “In the case of ethanol…dense structure.”: What about the formation of CO as a well-known intermediate in ethanol and formic acid electro-oxidation reactions? CO is known to poison Pt catalysts by strongly adsorbing on their surface.
7. Page 9 (last paragraph): I would suggest the authors to compare their results with a selection of those reported in the literature using MEAs (membrane electrode assemblies) prepared adopting conventional approaches for the catalytic layer, such as CCM and CCS (sputtering, spraying etc.), different types of membranes, experimental conditions etc. (in other words a comparison with the state-of-the-art MEAs). The advantages of their approach should be clearly emphasized.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors addressed a few of the issues pointed by the reviewers, but some weaknesses are still present in the manuscript. However, it is stated by the authors that the current health and safety regulations in their country do not allow for further measurements, which is understandable. Thus, and based on the fact that the overall quality of the work is acceptable for publication (despite the weaknesses noted during the first stage of the revision) I recommend acceptance and hope that the authors will manage to continue their research as soon as possible.